Application of Alum Sludge in Wastewater Treatment Processes: “Science” of Reuse and Reclamation Pathways

Green coagulation and flocculation: Scenedesmus algal extract-loaded chitosan/poly(vinyl alcohol) cryogel for effective water treatment

This study presents an eco-friendly approach to treat contaminated and turbid water through the development of cryogels loaded with bioactive compounds derived from Scenedesmus algal extract (ScAE) based on chitosan/poly(vinyl alcohol) (Cs/PVA) matrix. Scenedesmus sp., a green microalga known for its bioactive properties, was cultivated and processed to obtain extracts with coagulation potential. This extract was incorporated into cryogel at concentrations of 2, 4, 6, and 8 mL to improve coagulation and flocculation processes. Physicochemical analyses, including Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), confirmed the successful synthesis and structural integrity of ScAE-loaded cryogels, demonstrating uniform morphology, high porosity, and enhanced mechanical strength with increasing ScAE concentration. Significant results highlight the effectiveness of a 50 mg ScAE-loaded cryogel, which achieved significant reductions in turbidity, from 6 NTU to 1.6 NTU, and total suspended solids (TSS), from 16 mg/L to 6 mg/L, in water samples. The highest concentration cryogel (ScAE-8) also demonstrated a 62 % reduction in nitrate levels, underscoring its capability for broader contaminant removal. These results reveal that the ScAE-loaded cryogels not only provide an effective, biodegradable alternative to conventional chemical coagulants such as alum but also align with green chemistry approaches, potentially providing a sustainable solution for the large-scale water treatment facilities while lowering the negative environmental consequnces.

Making waves: Breaking the bottleneck of recycling drinking water treatment residue for practical engineering applications in water pollution control

Drinking water treatment residue (DWTR), an inevitable byproduct of water treatment plants, is typically recycled to control water pollution. DWTR poses a low environmental risk and has the potential to function as a functional material for various applications. However, the practical engineering applications of DWTR are limited. These limitations arise from a disconnect between fundamental research and the practical needs of engineering applications, creating a bottleneck for the effective recycling of DWTR. Previous studies have primarily focused on exploring potential DWTR recycling methods that reuse Al, Fe, Mn, Ca, Si, and organic C. However, the varying properties of DWTR obtained from different water treatment plants tend to differ with respect to potential recycling methods, confusing managers and engineers in using relevant knowledge to guide practical engineering applications. To address this challenge, the author advocates for a shift in research toward establishing guidelines that provide direct guidance for practical engineering applications of DWTR. The key components of these guidelines should include risk assessment, capability evaluation, and environmental application procedures with sustainability assessment to break the bottleneck associated with the recycling of DWTR.

Aluminosilicate and zeolitic materials synthesis using alum sludge from water treatment plants: Challenges and perspectives

Alum sludge (AS) is a by-product generated from drinking water treatment and produced in large amounts around the world. Its chemical composition makes this waste an emerging alternative source of silicon and aluminum for aluminosilicates or zeolite material production, which can add value to residues and contribute to the circular economy process on a global scale. In this sense, and considering the scarcity of information about AS, this review shows data collection about AS in different countries, including generation, chemical composition, and disposal information. The reuse of AS is discussed based on circular economy and the environmental gains derived from such approaches are highlighted, including the possibility of utilization with other residues (e.g., ash, bioproducts, etc). Moreover, this review shows and discusses the benefits and challenges of AS reuse in the synthesis process and how it can be a sustainable raw material for aluminosilicates and zeolite synthesis. The most common conditions (conventional or non-conventional) in zeolite synthesis from AS are mentioned and advantages, limitations and trends are discussed. The discussions and data presented can improve the AS management and reuse legislations, which certainly will collaborate with sustainable AS use and circular economy processes.

Aluminum Biorecovery from Wastewaters

Aluminum biorecovery is still at an early stage. However, a significant number of studies showing promising results already exist, although they have revealed problems that need to be solved so aluminum biorecovery can have a wider application and industrial upscaling. In this chapter, we revise the existing knowledge on the biorecovery of aluminum from different sources. We discuss the design, overall performance, advantages, technical problems, limitations, and possible future directions of the different biotechnological methods that have been reported so far. Aluminum biorecovery from different sources has been studied (i.e., solid wastes and primary sources of variable origin, wastewater with low concentrations of dissolved aluminum at pH-neutral or weakly acidic conditions, and acidic mine waters with high concentrations of dissolved aluminum and other metal(loid)s) and has shown that the process efficiency strongly depends on factors such as (1) the physicochemical properties of the source materials, (2) the physiological features of the used (micro)organisms, or (3) the biochemical process used. Bioleaching of aluminum from low-grade bauxite or red mud can much be achieved by a diverse range of organisms (e.g., fungi, bacteria) with different metabolic rates. Biorecovery of aluminum from wastewaters, e.g., domestic wastewater, acidic mine water, has also been accomplished by the use of microalgae, cyanobacteria (for domestic wastewater) or by sulfate-reducing bacteria (acidic mine water). In most of the cases, the drawback of the process is the requirement of controlled conditions which involves a continuous supply of oxygen or maintenance of anoxic conditions which make aluminum biorecovery challenging in terms of process design and economical value. Further studies should focus on studying these processes in comparison or in combination to existing economical processes to assess their feasibility.

Use of wastewater alum-coagulation sludge as a phosphorus fertiliser - a mini review

The use of aluminium (Al) salts, particularly alum, in coagulation is a widespread and conventional treatment method for eliminating pollutants, including phosphorus (P) which can cause eutrophication, from wastewater. However, a significant challenge of this process is the substantial amount of sludge generated, necessitating proper disposal. Historically, land disposal has been a common practice, but it poses potential issues for plant life on these lands. Despite the associated drawbacks, sludge contains elevated concentrations of vital plant nutrients like P and nitrogen, presenting an opportunity for beneficial use in agriculture. Given the imminent scarcity of P fertilizers due to the eventual depletion of high-grade P ores, this review explores the potential advantages and challenges of utilizing Al sludge as a P source for plants and proposes measures for its beneficial application. One primary concern with land application of Al sludge is its high levels of soluble Al, known to be toxic to plants, particularly in acidic soils. Another issue arises from the elevated Al concentration is P fixation and subsequently reducing P uptake by plants. To address these issues, soil treatment options such as lime, gypsum, and organic matter can be employed. Additionally, modifying the coagulation process by substituting part of the Al salts with cationic organic polymers proves effective in reducing the Al content of the sludge. The gradual release of P from sludge into the soil over time proves beneficial for plants with extended growth periods.

Management of selected waste generated during cable production

The subject of the research was the recovery of raw materials from waste generated in the production of cable insulation and the management of aluminum sludge. It was found that 49% (w/w) acetophenone, 6.8% (w/w) α-methylstyrene, and 17.2% (w/w) cumyl alcohol can be recovered from waste with a loss on ignition of 95% and used in various industries. A gas chromatograph equipped with a mass spectrometry detector was used to identify the recovered compounds. A waste distillation process was proposed to remove the water layer and obtain a concentrated acetophenone fraction. A method of neutralizing the water fraction and distillation residues is presented. The proposed waste management method is an alternative method to the currently used thermal transformation method. In turn, aluminum sludge was used to produce aluminum sulfate, which was used in the plant's sewage treatment plant as a coagulant. The effect of this action was a reduction of 67% in the content of total iron, 60% of trivalent iron, and 32% of chemical oxygen demand. The above-mentioned examples of waste management are part of a closed-loop waste management strategy.

Application of modified water treatment residuals in water and wastewater treatment: A review

Large quantities of sludge known as water treatment residuals (WTRs) are generated from water treatment facilities across the world. Various attempts have been made to reuse these residuals. Among the different applications of WTRs, their reuse in water and wastewater treatment has received more attention. However, direct application of raw WTRs is associated with some limitations. In the last decade, in order to improve their characteristics, numerous investigators have modified WTRs by different methods. This paper reviews the different methods applied to WTRs to enhance their characteristics. The effects of these modifications on their characteristics are explained. The applications of modified WTRs as a filtration/adsorption medium for treating textile/dye wastewater, groundwater containing different anionic and cationic pollutants, storm water runoff, and as a substrate in constructed wetlands are presented in detail. Future research needs are highlighted. The review clearly indicates the potential of different modification methods to improve the removal of a variety of pollutants by WTRs from water and wastewater.

Achieving win-win outcomes with cerium-loaded porous aluminum sludge hydrogel microspheres for enhanced phosphate removal

Breaking the technical bottleneck of traditional powdered adsorbent in phosphate adsorption application treatment, a macroscopic high adsorption performance aluminum sludge-based composite hydrogel material was constructed to synergistically solve the problems of water eutrophication and aluminum sludge resourcization. In this study, porous Ce-modified aluminum sludge hydrogel microspheres (Ce-AlS-SA) were prepared to improve the surface chemical structure and microscopic morphology of the macroscopic adsorbent material to enhance the adsorption capacity and achieve effective solid-liquid separation. The best adsorption performance of the material (Ce-AlS₁₂-SA₁) was obtained when the Ce-AlS: SA: Na₂CO₃ was 12:1:1, and obtained the optimal adsorption conditions by Response Surface Method (RSM) with 1.5 mg/L of the dosage, 4 of pH and 50 mg/L of C_phosphate. The maximum adsorption of 20.36 mg P/g was obtained by the Langmuir model at 303 K, which was 2.92 times more than raw sludge. According to the Freundlich and pseudo-second-order kinetic model, the adsorption process is chemisorption; the multi-stage adsorption process is reflected in the intraparticle diffusion and film diffusion models. The main mechanisms combined with the characterization analysis are electrostatic gravity, ligand exchange, and inner-sphere complexation. Meanwhile, Ce-AlS₁₂-SA₁ shows good resistance to interference in the coexistence of multiple ions. Therefore, this material can be recognized as a new material with in-depth, diversified and practical needs for resourceful utilization, which is expected to achieve extensive engineering applications in the future.

Ecologically Engineered Systems for Treating Agriculture Runoff by Integrating “Wastes” into Constructed Wetlands

Runoff from agricultural irrigation is contaminated and loaded with pesticides. Frequent toxic levels of pesticide detection in the ecosystem motivate scientists and engineers to diminish agro-chemicals flowing into the environment. Constructed wetland, CWs, treatments are a sustainable methodology of special interest since it possess a symbiosis value. Flytek (FT) pesticide use has increased at an unprecedented rate for crop production as well as an increase in runoff loaded with Flytek. This study introduces the use of constructed wetlands based on an alum- sludge substrate for the purpose of Flytek (FT) removal performance. The system is based on an adsorption column and a sludge cake coupled with gravel acting as a carrier in order to be an adsorption bed and filtration system for Flytek removal. The structure, morphology and characteristics of the adsorption bed material “alum sludge” were characterized using X-ray diffraction spectroscopy and Scanning Electron Microscope (SEM). Additionally, Fourier-Transform infrared spectroscopy (FTIR) was explored. The experimental results revealed that a vertical flow constructed wetland is significant in eliminating the Flytek pesticide. However, the amount and height of sludge in a wetlands column affects its removal efficiency with the optimal removal (96%) being linked to the presence of sludge in 80%. Moreover, temperature, pH and the FT load showed a significant effect in removals, with the optimal operating conditions being recorded at 7.2 pH, 26 °C and 100 ppm of FT. The kinetic modeling is also investigated to validate the practical life applications and designs, and the results verified the reaction follows the pseudo 2nd-order reaction kinetic model according to the correlation coefficient factor. Furthermore, according to the isotherm model results the scheme follows the Freundlich isotherm model. Such preliminarily data of a gravel-alum-sludge-adsorption-column scheme is a good indicator in developing a constructed wetland facility being a good candidate for controlling agriculture effluent streams.

Plant-based coagulants/flocculants: characteristics, mechanisms, and possible utilization in treating aquaculture effluent and benefiting from the recovered nutrients

The increasing intensification of the aquaculture industry requires the development of new strategies to reduce the negative impacts of wastewater on the environment. Plant-based coagulants/flocculants, regarded as one of the environmentally friendly technologies for wastewater treatment, show good performance in the removal of suspended solids from wastewater. The aforementioned technology involves the utilization of plants as coagulants/flocculants in the treatment process and produces nontoxic sludge as treatment by-products. The produced sludge could be converted into valuable compounds used in agriculture. This review summarizes coagulation-flocculation by using plant-based coagulants/flocculants, its mechanisms, operational factors that control the treatment process, and its application in the treatment of wastewater, especially aquaculture effluent. Moreover, this work discusses the potential utilization of aquaculture sludge as a valuable compound used in agriculture. The presented review aims to emphasize the potential of using plant-based coagulants/flocculants in the treatment of aquaculture effluent and explore the potential of using the produced sludge as fertilizer for plants to solve problems related to sludge handling and the toxicity of inorganic coagulants in a recirculating aquaculture system. This paper concluded that utilization of recovered nutrients in the form of solids is feasible for agricultural purposes, while a hydroponic system can be used to reclaim the nutrients in the form of solution.

Washing and Heat Treatment of Aluminum-Based Drinking Water Treatment Residuals to Optimize Phosphorus Sorption and Nitrogen Leaching: Considerations for Lake Restoration

Drinking water treatment residuals (DWTRs) generated during drinking water treatment have been proposed for use in lake restoration as a solid-phase sorbent to inactivate phosphorus (P) in lake sediment. However, treatments that minimize leaching of nitrogen (N) and optimize P sorption capacity may be necessary prior to use. This study assessed seven different treatment methods, including washing and heat treatments at different temperatures and with and without oxygen limitation, among two DWTRs from Thailand. Results showed that oxygen-limited heat treatment at 600 °C substantially reduced N leaching (<0.2 mg/kg TKN) while also improving P sorption capacity (increase of 18–32% compared to untreated DWTR) to a maximum of 45.7 mg P/kg. Washing with deionized water reduced N leaching if a sufficient volume was used but did not improve P sorption. Heating at 200 °C with or without the presence of oxygen did not improve N leaching or P sorption. Regression of P sorption parameters from a two-surface Langmuir isotherm against physio-chemical properties indicated that oxalate-extractable (i.e., amorphous) aluminum and iron were significantly associated with total P sorption capacity (R2 = 0.94), but micropores and oxalate-extractable P modulated the P sorption from high-affinity to low-affinity mechanisms. In conclusion, this study confirmed the importance of amorphous aluminum in DWTRs for inactivating P, and the results suggest that high-temperature treatment under oxygen-limited conditions may be the most reliable way to optimize DWTRs for environmental remediation applications.